I think everyone has a favourite mastering weapon, that last minute icing for the cake. For me, I'd say it's Venn's V-Clip. I don't use it for all projects, but when it comes to taming transients and smoothing out levels transparently, V-Clip is it. Its visualization alone is worth the price of admission. The fact that there's also oversampling makes it a winner, especially if you use V-Clip for its distortion and saturation abilities. Definitely a keeper.